[llvm] r314971 - [InstCombine] Fix a vector splat handling bug in transformZExtICmp.

[Craig Topper via llvm-commits]

Author: ctopper
Date: Thu Oct  5 00:59:11 2017
New Revision: 314971

URL: http://llvm.org/viewvc/llvm-project?rev=314971&view=rev
Log:
[InstCombine] Fix a vector splat handling bug in transformZExtICmp.

We were using an i1 type and then zero extending to a vector. Instead just create the 0/1 directly as a ConstantInt with the correct type. No need to ask ConstantExpr to zero extend for us.

This bug is a bit tricky to hit because it requires us to visit a zext of an icmp that would normally be simplified to true/false, but that icmp hasnt' been visited yet. In the test case this zext and icmp were created by visiting a udiv and due to worklist ordering we got to the zext first.

Fixes PR34841.

Modified:
    llvm/trunk/lib/Transforms/InstCombine/InstCombineCasts.cpp
    llvm/trunk/test/Transforms/InstCombine/div.ll

Modified: llvm/trunk/lib/Transforms/InstCombine/InstCombineCasts.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/InstCombine/InstCombineCasts.cpp?rev=314971&r1=314970&r2=314971&view=diff
==============================================================================
--- llvm/trunk/lib/Transforms/InstCombine/InstCombineCasts.cpp (original)
+++ llvm/trunk/lib/Transforms/InstCombine/InstCombineCasts.cpp Thu Oct  5 00:59:11 2017
@@ -818,9 +818,7 @@ Instruction *InstCombiner::transformZExt
         if (!Op1CV->isNullValue() && (*Op1CV != KnownZeroMask)) {
           // (X&4) == 2 --> false
           // (X&4) != 2 --> true
-          Constant *Res = ConstantInt::get(Type::getInt1Ty(CI.getContext()),
-                                           isNE);
-          Res = ConstantExpr::getZExt(Res, CI.getType());
+          Constant *Res = ConstantInt::get(CI.getType(), isNE);
           return replaceInstUsesWith(CI, Res);
         }
 

Modified: llvm/trunk/test/Transforms/InstCombine/div.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/InstCombine/div.ll?rev=314971&r1=314970&r2=314971&view=diff
==============================================================================
--- llvm/trunk/test/Transforms/InstCombine/div.ll (original)
+++ llvm/trunk/test/Transforms/InstCombine/div.ll Thu Oct  5 00:59:11 2017
@@ -553,3 +553,12 @@ define i32 @shrink_no3(i16 %x) {
   ret i32 %div
 }
 
+; This previously crashed when trying to simplify the zext/icmp this becomes.
+define <2 x i8> @PR34841(<2 x i8> %x) {
+; CHECK-LABEL: @PR34841(
+; CHECK-NEXT:    ret <2 x i8> zeroinitializer
+;
+  %neg = and <2 x i8> %x, <i8 2, i8 2>
+  %div = udiv <2 x i8> <i8 1, i8 1>, %neg
+  ret <2 x i8> %div
+}